1. Field of the Invention
The present invention relates to a time-interleaved bandpass Δ-Σ modulator (hereinafter, referred to as “a delta-sigma modulator”). More particularly, this invention relates to a delta-sigma modulator including a plurality of channel blocks, of which the phase of the lock frequencies is different from each other, so as to reduce a clock frequency.
2. Related Prior Art
A delta-sigma modulator generally includes a lowpass modulator and a bandpass modulator. The lowpass modulator is used for audio devices, while the bandpass modulator is used for radio communication. The delta-sigma modulator may be composed of a continuous-time circuit or a discrete-time circuit, with reference to FIG. 1a and FIG. 1b. A bandpass delta-sigma modulator in FIG. 1b samples the intermediate-frequency (IF) as many as four times, and removes quantization noise (this is referred to as shaping). In the modulator, because the noise is shaped at the input signal within the desired band, a high signal-to-noise ratio (SNR) can be achieved at the input signal on the desired band.
A bandpass delta-sigma modulator that is implemented by a continuous-time circuit (see FIG. 1a) has an advantage that it can operate in a high frequency band. However, it also has a disadvantage that the user must tune a center frequency. In the case of a bandpass delta-sigma modulator that is embodied by discrete-time circuit as in FIG. 1b, such as a switched capacitor circuit, however accurate and reliable it may be, it cannot be operated on the commonly used high frequency IF band, because it must use a clock frequency four times higher than the input signal.